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Date: Wed, 9 Oct 2019 20:51:56 +0000
From: Martin Lau <kafai@...com>
To: Alexei Starovoitov <ast@...nel.org>
CC: "davem@...emloft.net" <davem@...emloft.net>,
"daniel@...earbox.net" <daniel@...earbox.net>,
"x86@...nel.org" <x86@...nel.org>,
"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
"bpf@...r.kernel.org" <bpf@...r.kernel.org>,
Kernel Team <Kernel-team@...com>
Subject: Re: [PATCH bpf-next 03/10] bpf: process in-kernel BTF
On Fri, Oct 04, 2019 at 10:03:07PM -0700, Alexei Starovoitov wrote:
> If in-kernel BTF exists parse it and prepare 'struct btf *btf_vmlinux'
> for further use by the verifier.
> In-kernel BTF is trusted just like kallsyms and other build artifacts
> embedded into vmlinux.
> Yet run this BTF image through BTF verifier to make sure
> that it is valid and it wasn't mangled during the build.
>
> Signed-off-by: Alexei Starovoitov <ast@...nel.org>
> ---
> include/linux/bpf_verifier.h | 4 ++-
> include/linux/btf.h | 1 +
> kernel/bpf/btf.c | 66 ++++++++++++++++++++++++++++++++++++
> kernel/bpf/verifier.c | 18 ++++++++++
> 4 files changed, 88 insertions(+), 1 deletion(-)
>
> diff --git a/include/linux/bpf_verifier.h b/include/linux/bpf_verifier.h
> index 26a6d58ca78c..432ba8977a0a 100644
> --- a/include/linux/bpf_verifier.h
> +++ b/include/linux/bpf_verifier.h
> @@ -330,10 +330,12 @@ static inline bool bpf_verifier_log_full(const struct bpf_verifier_log *log)
> #define BPF_LOG_STATS 4
> #define BPF_LOG_LEVEL (BPF_LOG_LEVEL1 | BPF_LOG_LEVEL2)
> #define BPF_LOG_MASK (BPF_LOG_LEVEL | BPF_LOG_STATS)
> +#define BPF_LOG_KERNEL (BPF_LOG_MASK + 1)
>
> static inline bool bpf_verifier_log_needed(const struct bpf_verifier_log *log)
> {
> - return log->level && log->ubuf && !bpf_verifier_log_full(log);
> + return (log->level && log->ubuf && !bpf_verifier_log_full(log)) ||
> + log->level == BPF_LOG_KERNEL;
> }
>
> #define BPF_MAX_SUBPROGS 256
> diff --git a/include/linux/btf.h b/include/linux/btf.h
> index 64cdf2a23d42..55d43bc856be 100644
> --- a/include/linux/btf.h
> +++ b/include/linux/btf.h
> @@ -56,6 +56,7 @@ bool btf_type_is_void(const struct btf_type *t);
> #ifdef CONFIG_BPF_SYSCALL
> const struct btf_type *btf_type_by_id(const struct btf *btf, u32 type_id);
> const char *btf_name_by_offset(const struct btf *btf, u32 offset);
> +struct btf *btf_parse_vmlinux(void);
> #else
> static inline const struct btf_type *btf_type_by_id(const struct btf *btf,
> u32 type_id)
> diff --git a/kernel/bpf/btf.c b/kernel/bpf/btf.c
> index 29c7c06c6bd6..848f9d4b9d7e 100644
> --- a/kernel/bpf/btf.c
> +++ b/kernel/bpf/btf.c
> @@ -698,6 +698,9 @@ __printf(4, 5) static void __btf_verifier_log_type(struct btf_verifier_env *env,
> if (!bpf_verifier_log_needed(log))
> return;
>
> + if (log->level == BPF_LOG_KERNEL && !fmt)
> + return;
> +
> __btf_verifier_log(log, "[%u] %s %s%s",
> env->log_type_id,
> btf_kind_str[kind],
> @@ -735,6 +738,8 @@ static void btf_verifier_log_member(struct btf_verifier_env *env,
> if (!bpf_verifier_log_needed(log))
> return;
>
> + if (log->level == BPF_LOG_KERNEL && !fmt)
> + return;
> /* The CHECK_META phase already did a btf dump.
> *
> * If member is logged again, it must hit an error in
> @@ -777,6 +782,8 @@ static void btf_verifier_log_vsi(struct btf_verifier_env *env,
>
> if (!bpf_verifier_log_needed(log))
> return;
> + if (log->level == BPF_LOG_KERNEL && !fmt)
> + return;
> if (env->phase != CHECK_META)
> btf_verifier_log_type(env, datasec_type, NULL);
>
> @@ -802,6 +809,8 @@ static void btf_verifier_log_hdr(struct btf_verifier_env *env,
> if (!bpf_verifier_log_needed(log))
> return;
>
> + if (log->level == BPF_LOG_KERNEL)
> + return;
> hdr = &btf->hdr;
> __btf_verifier_log(log, "magic: 0x%x\n", hdr->magic);
> __btf_verifier_log(log, "version: %u\n", hdr->version);
> @@ -2406,6 +2415,8 @@ static s32 btf_enum_check_meta(struct btf_verifier_env *env,
> }
>
>
> + if (env->log.level == BPF_LOG_KERNEL)
> + continue;
> btf_verifier_log(env, "\t%s val=%d\n",
> __btf_name_by_offset(btf, enums[i].name_off),
> enums[i].val);
> @@ -3367,6 +3378,61 @@ static struct btf *btf_parse(void __user *btf_data, u32 btf_data_size,
> return ERR_PTR(err);
> }
>
> +extern char __weak _binary__btf_vmlinux_bin_start[];
> +extern char __weak _binary__btf_vmlinux_bin_end[];
> +
> +struct btf *btf_parse_vmlinux(void)
> +{
> + struct btf_verifier_env *env = NULL;
> + struct bpf_verifier_log *log;
> + struct btf *btf = NULL;
> + int err;
> +
> + env = kzalloc(sizeof(*env), GFP_KERNEL | __GFP_NOWARN);
> + if (!env)
> + return ERR_PTR(-ENOMEM);
> +
> + log = &env->log;
> + log->level = BPF_LOG_KERNEL;
> +
> + btf = kzalloc(sizeof(*btf), GFP_KERNEL | __GFP_NOWARN);
> + if (!btf) {
> + err = -ENOMEM;
> + goto errout;
> + }
> + env->btf = btf;
> +
> + btf->data = _binary__btf_vmlinux_bin_start;
> + btf->data_size = _binary__btf_vmlinux_bin_end -
> + _binary__btf_vmlinux_bin_start;
> +
> + err = btf_parse_hdr(env);
> + if (err)
> + goto errout;
> +
> + btf->nohdr_data = btf->data + btf->hdr.hdr_len;
> +
> + err = btf_parse_str_sec(env);
> + if (err)
> + goto errout;
> +
> + err = btf_check_all_metas(env);
> + if (err)
> + goto errout;
> +
Considering btf_vmlinux is already safe, any concern in making an extra
call to btf_check_all_types()?
Having resolved_ids and resolved_sizes available will
be handy in my later patch.
> + btf_verifier_env_free(env);
> + refcount_set(&btf->refcnt, 1);
> + return btf;
> +
> +errout:
> + btf_verifier_env_free(env);
> + if (btf) {
> + kvfree(btf->types);
> + kfree(btf);
> + }
> + return ERR_PTR(err);
> +}
> +
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